Attenuation of drill cablesMemoirs of National Institute of Polar Research, Special Issue, No. 56, p. 206-208, 2002
N.S. Gundestrup, S.J. Johnsen
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen.
The frequemcy characteristics of a drilll cable determines both the type of communication that can be used between a drill or logger and the surface, as well as the maximum rate of information that can be transferred. In order to revise the design, the attenuation of the cable was measured. The result was far from the characteristics of a coaxial cable. At medium audio frequencies, the attenuation was quite low. However at both low and high frequencies, the attenuation increased significantly, and the high frequency cut off could be approximated by a 3-order low pass filter with a cut off frequency of 8 kHz. For comparison, the attenuation of a similar size coaxial type cable will be in order of 1 dB/300 m at 150 kHz increasing to 2 dB/300 m at 1MHz. If a bandwidth higher than 10 kHz is required for a 4 km long oceanographic type electromechanical steel armoured cable, this has to be of coaxial construction with a shield separated from the armour.